In the technical field of medical radiology, computer tomographs have gained increasingly in importance in recent years. In computed tomography, x-ray radiation is irradiated from a radiation source towards an object to be examined, as a rule a patient, and, on the basis of the attenuation of the X-ray radiation after this has passed through the object to be examined, an image is produced on a monitor. In this process, the radiation source is moved around the object to be examined and from different positions records images of individual slices of the object to be examined. The individual slice images or tomograms can finally be added together and produce a three-dimensional image on the monitor of the object to be examined. Specifically in the case of computed tomography recordings of the lung, the objective is the identification of abnormal tissue, known as nodules, in the lung at an early stage. In order to prepare an analyzable image of the lung, other structures apart from the lung, for instance the thoracic cage or the heart, are suppressed in the slice images. This is achieved by essentially known segmentation methods, in which slice images of structures of the object to be examined are subtracted from one another and individual structures are thereby removed from the resulting image. When two slice images, which approximately congruently show a structure to be removed, are arranged one on top of the other and the gray-scale values of the slice images are subtracted from each other, the image of the structure is removed from the two slice images. In a special process, interfering structures are removed from the image, so that only the lung cavity and the blood vessels appear. The blood vessels are in this case rendered recognizable in the X-ray image essentially by means of a contrast medium injected into the patient and in terms of contrast with respect to the background, here the lung cavity, stand out clearly. The problem with this process, however, is that the contrast between abnormal tissue and the blood vessels containing the contrast medium is low, the attenuation values, also known as Hounsfield values, received by the detector device of the computer tomograph do not differ significantly from one another. In particular, abnormal tissue that lies close to or on the blood vessels is not identified in the images owing to the similar gray-scale values of the abnormal tissue and the blood vessels.